Did they change the cooling system again, or did I misunderstood their previous talk about using only metal and transpiration cooling?

The transpiration was only for the hottest parts. A conventional passive heatshield was to be used for the cooler locations. My understanding is there is no change. Or maybe that was just an assumption on my part. SpaceX talked a lot about the transpiration cooling but I got the impression that wasn't the entire thermal protection system.

There was also talk that seemed to indicate cooling of the outer stainless layer with circulating fluid. Possibly this in addition to the transpiration or just something they were thinking of back then. I would imagine that would also need to be vented to dump the heat though.

Those launch complexes are at NASA's Kennedy Space Center at Cape Canaveral, Florida. The U.S. Board of Geographic Names responded on October 9, 1973 by agreeing to officially recognize the name change from Cape Kennedy to Cape Canaveral at the national level. The name John F. Kennedy Space Center, NASA remained the same. End of nit picking.

Those hex tiles undergoing a torch test appear to be PICA-X tiles that will protect most of the windward side of Starship. Elon mentioned that he anticipates having to use his transpiration cooling option on the really hot spots where ablation rate is large. This probably refers to the windward side of Starship from the nose downward say 5-10 meters along the fuselage.

I'm anxiously awaiting details on the way he plans to attach these hex tiles to Starship. I don't think Elon wants to use adhesives as was done for the tiles on the Shuttle Orbiter. My guess is that his designers have come up with mechanical fasteners that will do the job.

The hex titles do not look like pica-x. Also pica-x is ablative which wouldn't fit with SpaceX's plans of gas and go. It is entirely possible the hex tiles are simply a high temperature steel. Making them into hexes would allow easy replacement as SpaceX learns and evolves what areas need beefed up thermal protection.

Got to admit that "well let's fly it see what burns off and then stick some cooling there" is pure SpaceX engineering. Models only go so far, might as well start iterative practical testing sooner rather than later.

Off the topic a bit: South Padre Island. If I weren't so entrenched with where I am now I'd head over there and set up a restaurant/bar/whatever themed to service space(X) buffs. But I'd have needed to start that about two years ago -- I imagine local rents and land values are already skyrocketing, so to speak...

So if the main roadway is considered safe enough that residents can still use it, on what grounds is it being closed to non-residents? I get why Elon might not want an audience, but is that how America operates— a billionaire wants some privacy so the public can no longer use a road they paid for?

Why is this being down-voted? While not directly related to the Starship development I find this question very interesting.

Did and the OP miss something in the article that explains this?

Closing public property temporarily for safety during commercial operations is common practice. In particular, this is allowed by Texas law and has to be approved by county officials.

Its just like sidewalks or roads being closed when doing heavy-lift operations onto city rooftops.

Roads are also sometimes closed for safety during severe weather conditions, such as blizzards or from flooding . No one complains about this being an unwarranted public subsidy of old man winter, or delves into his race, gender or net worth as contributing factors.

I've noted that alt-right trolls who want to give the false impression of being an "SJW" for false-flag purposes have a habit of doing this. With all the nuance of someone who glanced at the packaging and threw away the manual, they throw in ridiculously out-of-context "woke" statements and then fail to understand why the "other side" downvotes them instead of flocking to support.

Not saying that's definitely the case here, of course. It might genuinely be the case that they have no idea what they're talking about.

Did they change the cooling system again, or did I misunderstood their previous talk about using only metal and transpiration cooling?

The transpiration was only for the hottest parts. A conventional passive heatshield was to be used for the cooler locations. My understanding is there is no change. Or maybe that was just an assumption on my part. SpaceX talked a lot about the transpiration cooling but I got the impression that wasn't the entire thermal protection system.

There was also talk that seemed to indicate cooling of the outer stainless layer with circulating fluid. Possibly this in addition to the transpiration or just something they were thinking of back then. I would imagine that would also need to be vented to dump the heat though.

That heat may be part of the driving force behind the transpiration.

I see no reason why it wouldn't be, they could also put some of it into the giant cold sink that takes up the bottom half of the ship, which will increase the pressure there, which can be used to drive some more fluid through the system..

Although it's the only one officially disclosed, I'd be shocked if they don't start flying a satellite deployment Starship first, and do a number of test flights of the crew version before the Dear Moon mission.

Many space industry companies and space hotels will want to go up using the starship too, either before or after the moon flight.

I'm still wondering when methane went from being a combustable to a coolant. I guess a flame cools, but a flame it is.

Methane-air flames at sub-atmospheric pressures are quite cold compared to what high-temperature steel can manage. Of course, if the methane does ignite, the combustion gases will expand and push the air boundary layer away. And since that boundary layer is plasma, that's a win-win.

I've noted that alt-right trolls who want to give the false impression of being an "SJW" for false-flag purposes have a habit of doing this. With all the nuance of someone who glanced at the packaging and threw away the manual, they throw in ridiculously out-of-context "woke" statements and then fail to understand why the "other side" downvotes them instead of flocking to support.

Not saying that's definitely the case here, of course. It might genuinely be the case that they have no idea what they're talking about.

That's been going on for decades. They attempt to get comments so they can then turn and say "See? The Librils are hypocrites!" Since most their 'thinking' is projection anyway, they fail miserably at masquerade.

I'm still wondering when methane went from being a combustable to a coolant. I guess a flame cools, but a flame it is.

The earliest reference I can find is THERMAL FEASIBILITY OF USING METHANE OR HYDROGEN FUEL FOR DIRECT COOLING OF A FIRST-STAGE TURBINE STATOR, NASA Technical Note D-6042, from October 1970, so almost 50 years now.

The SR-71 (if not other aircraft) used its fuel to cool the leading edge of the wings. It wasn't transpiration cooling, but active cooling using a fuel is not new. Hell, that's why RP-1 isn't just kerosene. It needed to withstand thermal breakdown when used to cool the nozzle and other combustor parts.

In my non-technical mind, I compare this with the approach pioneered by Burt Rutan and SpaceShipOne in the Virgin Galactic program, which used a deformable structure to massively increase drag such that the vehicle's speed bleeds away before it gets to a part of the atmosphere where re-heating becomes a concern.

You’re looking at an absolutely massive difference in energy levels. SSO/SST peaks out at around Mach 3. Super Heavy is going to re-enter somewhere around Mach 8, using the engine exhaust as a “virtual” heat shield during peak heating, as does the Falcon 9 first stage. Starship is going to re-enter at somewhere between Mach 25 and Mach 40, depending on where it’s coming from.

But I'm very interested to ask if a combination of the current SpaceX design for re-usability, coupled with maybe even disposable, deformable drag structures [think grid fins on steroids] might have been an avenue worth exploring. I make this observation in the context of Elon's statement that he needs Starship to make an instant return-to-use [i.e. allow it to cool and then just pump it full of fuel before relaunch], but that doesn't preclude disposable aerofoils.

Such drag structures add lots of mass. It you are doing horizontal landing, well then you have that mass anyway, so it only makes sense to use them that way.

Note that SSO’s design doesn’t provide a high surface area for drag, but rather makes that high drag orientation passively stable. Starship is using its legs and canards as drag flaps to maintain attitude. Shuttle and Buran used large aft planes and RCS to maintain attitude. In other words, everyone does it, but SSO did it in a way that didn’t require fly-by-wire, due to Burt Rutan’s feelings on the matter.

It’s not my world view, it’s Elon’s. He’s publicly stated in televised interviews that he feels no need to obey or respect the chair of Tesla’s board, and would simply call a shareholder vote if she ever says anything. Would he talk about a fellow white billionaire male such as Larry Ellison that way? Maybe, but he has never done so even once.

Elon doesn’t respect the person that the SEC forced Tesla to put in place and you’re saying it’s because he’s a white man? Jesus does it hurt when you try to twist everything to fit into a white man bad worldview?

The SEC didn’t force Elon to appoint someone he didn’t respect. That was Elon’s choice. It seems likely he appointed a woman for optics / publicity even though he couldn’t work with her. The lack of respect isn’t restricted to public bravado. He also makes idiotic business decisions like closing stores without checking to see if he signed an ongoing lease on the space without consulting with her. Those are the kinds of high level strategy decisions a board chair would normally get to be involved in.

How about you link to some proof that he does not respect Robyn Denholm? I would be interested to know why she was on the board for 5 years, he did not respect her, and then she not only stayed on but got promoted to chairwoman ... by Elon Musk. Do you think your claims make any kind of sense whatsoever? Googling does not bring up anything for your statement which would be astonishing if your claims are remotely true.

Or is this just stupid bullshit for a dumb world view? Musk is on record as not respecting the Short Enrichment Commision. Are you confused which is which? Or does it just not matter. Musk is a white male and automatically as evil as a cartoon Hollywood rich villain?

You claim he would go bananas if she ever "said anything"? This is just donkey shit. What he said is precisely this: as majority owner the board can not compel him to do anything he does not want to do. Do you even know what that means and why it is true for any company? Do you know why that has nothing to do with his personal relations with a long time board member? Or do you think she was a board member and they had good relations but then because he chose her to stand in for him he suddenly hates her guts? WTF man. Prosecute irrational beliefs somewhere not fact based like Ars. Maybe politico or youtube will care.

If part of the heat shield's functionality relies on high reflectivity, won't at least soot need to be washed off before re-flying?

How does this work with the "0 refurbishing" goal?

What soot? The lack of ablative TPS means much cleaner reentry and the landing burn is done with methane which burns much cleaner than the RP1 used by Falcon 9.

Maybe no soot, but it will likely oxidize and darken. That shouldn't affect it particularly -- darker means it can radiate heat as well as absorb it more effectively.

As for "but it's *stainless*", many stainless steels are stainless because they oxidize more aggressively than plain steel, but form an impervious oxide layer (like aluminum). E.g., chromium steels are 'active surface' stainless (they tend to be used for applications where hardness and keeping an edge is required).

I'm still wondering when methane went from being a combustable to a coolant. I guess a flame cools, but a flame it is.

You need oxygen to combust methane. SpaceX already uses methane as a coolant in the Raptor, to keep the nozzle and combustion chamber form melting. The also spray fuel inside the Raptor combustion chamber as a coolant. As long as it doesn't have access to much oxygen, it cools fine.

At Mach 25 and a partial pressure of oxygen of about 0, there won't be much combustion of the coolant during reentry.

I suspect all the methane will burn. Even at near zero bar, the fact there's drag means there's 21% oxygen entering the plasma field. And since it's a plasma, you've got all sorts of energetic radicals ready to instantly ignite the methane molecules. Of course, you have almost a perfect diffusion flame so the flame front is going to occur where methane and oxygen concentrations fall to zero. That could be many millimeters from the skin.

I'm still wondering when methane went from being a combustable to a coolant. I guess a flame cools, but a flame it is.

It starts as a very cold gas. It exits the skin as a hot gas and quickly turns into a very hot gas. Some of it may burn with the very low concentration of oxygen in the thin air plasma miles behind the SS but that is irrelevant to cooling the SS.

It will make a perfect diffusion flame on the leading edge I bet. And compared to the potential thermal energy that would be transferred by direct contact with the plasma bow shock, the chemical energy release from that combustion will be trivial.

I've noted that alt-right trolls who want to give the false impression of being an "SJW" for false-flag purposes have a habit of doing this. With all the nuance of someone who glanced at the packaging and threw away the manual, they throw in ridiculously out-of-context "woke" statements and then fail to understand why the "other side" downvotes them instead of flocking to support.

Not saying that's definitely the case here, of course. It might genuinely be the case that they have no idea what they're talking about.

That's been going on for decades. They attempt to get comments so they can then turn and say "See? The Librils are hypocrites!" Since most their 'thinking' is projection anyway, they fail miserably at masquerade.

If pkirvan is genuine, which I think is true, than these words must be devastating.

In my non-technical mind, I compare this with the approach pioneered by Burt Rutan and SpaceShipOne in the Virgin Galactic program, which used a deformable structure to massively increase drag such that the vehicle's speed bleeds away before it gets to a part of the atmosphere where re-heating becomes a concern.

You’re looking at an absolutely massive difference in energy levels. SSO/SST peaks out at around Mach 3. Super Heavy is going to re-enter somewhere around Mach 8, using the engine exhaust as a “virtual” heat shield during peak heating, as does the Falcon 9 first stage. Starship is going to re-enter at somewhere between Mach 25 and Mach 40, depending on where it’s coming from.

But I'm very interested to ask if a combination of the current SpaceX design for re-usability, coupled with maybe even disposable, deformable drag structures [think grid fins on steroids] might have been an avenue worth exploring. I make this observation in the context of Elon's statement that he needs Starship to make an instant return-to-use [i.e. allow it to cool and then just pump it full of fuel before relaunch], but that doesn't preclude disposable aerofoils.

Such drag structures add lots of mass. It you are doing horizontal landing, well then you have that mass anyway, so it only makes sense to use them that way.

Note that SSO’s design doesn’t provide a high surface area for drag, but rather makes that high drag orientation passively stable. Starship is using its legs and canards as drag flaps to maintain attitude. Shuttle and Buran used large aft planes and RCS to maintain attitude. In other words, everyone does it, but SSO did it in a way that didn’t require fly-by-wire, due to Burt Rutan’s feelings on the matter.

Starship uses a blunt body entry profile, not a lifting body it has the surface area of the propellant tanks and the payload section to provide a high surface area to mass ratio

Did they change the cooling system again, or did I misunderstood their previous talk about using only metal and transpiration cooling?

The transpiration was only for the hottest parts. A conventional passive heatshield was to be used for the cooler locations. My understanding is there is no change. Or maybe that was just an assumption on my part. SpaceX talked a lot about the transpiration cooling but I got the impression that wasn't the entire thermal protection system.

There was also talk that seemed to indicate cooling of the outer stainless layer with circulating fluid. Possibly this in addition to the transpiration or just something they were thinking of back then. I would imagine that would also need to be vented to dump the heat though.

There is no circulation in the Starship heat shield as far as we know. In transpiration cooling the coolant gets pushed through the skin and dumped overboard. Transpiration is like sweating, circulation is like blood flow.

Right I get the differences. I am just wondering if they are using both. The tweets are not exactly super specific. Radiative cooling across 80% and active cooling on 20%. Is the vapor enough to handle all of it or do you also need to just generally cool the skin down from inside as well? Elon did say you need cryogenic liquid, the specific heat matters. Also, the cooling need is 300 degrees down into the tolerance range of the steel (around 1450 Kelvin). That still leaves an incredibly hot shell wrapped around much more delicate internal structures and fuel.

This has been tested a long time ago and the failure mode then was rapid vaporization of the test vehicle in the wind tunnel from as little as single clogged pores. Is the SpaceX design proof against that, is it susceptible to bird poop clogging? Can you rely on sweat everywhere or do you need additional cooling or a backup scheme to spread out a hot spot instead of letting it burn through?

See, I'd think the inner shell will be the structurally sound one. It's the one that's holding the cryo fuels after all. The outer shell may be thin-walled hex tiles that barely support any load one launch. The dynamic pressure from entry won't be that high in comparison to the thrust loads through the main structure.

In my non-technical mind, I compare this with the approach pioneered by Burt Rutan and SpaceShipOne in the Virgin Galactic program, which used a deformable structure to massively increase drag such that the vehicle's speed bleeds away before it gets to a part of the atmosphere where re-heating becomes a concern.

You’re looking at an absolutely massive difference in energy levels. SSO/SST peaks out at around Mach 3. Super Heavy is going to re-enter somewhere around Mach 8, using the engine exhaust as a “virtual” heat shield during peak heating, as does the Falcon 9 first stage. Starship is going to re-enter at somewhere between Mach 25 and Mach 40, depending on where it’s coming from.

But I'm very interested to ask if a combination of the current SpaceX design for re-usability, coupled with maybe even disposable, deformable drag structures [think grid fins on steroids] might have been an avenue worth exploring. I make this observation in the context of Elon's statement that he needs Starship to make an instant return-to-use [i.e. allow it to cool and then just pump it full of fuel before relaunch], but that doesn't preclude disposable aerofoils.

Such drag structures add lots of mass. It you are doing horizontal landing, well then you have that mass anyway, so it only makes sense to use them that way.

Note that SSO’s design doesn’t provide a high surface area for drag, but rather makes that high drag orientation passively stable. Starship is using its legs and canards as drag flaps to maintain attitude. Shuttle and Buran used large aft planes and RCS to maintain attitude. In other words, everyone does it, but SSO did it in a way that didn’t require fly-by-wire, due to Burt Rutan’s feelings on the matter.

Starship uses a blunt body entry profile, not a lifting body it has the surface area of the propellant tanks and the payload section to provide a high surface area to mass ratio

SSO flys at something like 70deg AOA, and even though Shuttle and Shuttleski were much lower, they were still in deep stall and not behaving anything like an airfoil.

I'm still wondering when methane went from being a combustable to a coolant. I guess a flame cools, but a flame it is.

The earliest reference I can find is THERMAL FEASIBILITY OF USING METHANE OR HYDROGEN FUEL FOR DIRECT COOLING OF A FIRST-STAGE TURBINE STATOR, NASA Technical Note D-6042, from October 1970, so almost 50 years now.

The SR-71 (if not other aircraft) used its fuel to cool the leading edge of the wings. It wasn't transpiration cooling, but active cooling using a fuel is not new. Hell, that's why RP-1 isn't just kerosene. It needed to withstand thermal breakdown when used to cool the nozzle and other combustor parts.

Of course, the JP-7 used by the Blackbirds was pretty much non-flammable without a shot of TEB.

I've noted that alt-right trolls who want to give the false impression of being an "SJW" for false-flag purposes have a habit of doing this. With all the nuance of someone who glanced at the packaging and threw away the manual, they throw in ridiculously out-of-context "woke" statements and then fail to understand why the "other side" downvotes them instead of flocking to support.

Not saying that's definitely the case here, of course. It might genuinely be the case that they have no idea what they're talking about.

That's been going on for decades. They attempt to get comments so they can then turn and say "See? The Librils are hypocrites!" Since most their 'thinking' is projection anyway, they fail miserably at masquerade.

If pkirvan is genuine, which I think is true, than these words must be devastating.

I'm still wondering when methane went from being a combustable to a coolant. I guess a flame cools, but a flame it is.

The earliest reference I can find is THERMAL FEASIBILITY OF USING METHANE OR HYDROGEN FUEL FOR DIRECT COOLING OF A FIRST-STAGE TURBINE STATOR, NASA Technical Note D-6042, from October 1970, so almost 50 years now.

The SR-71 (if not other aircraft) used its fuel to cool the leading edge of the wings. It wasn't transpiration cooling, but active cooling using a fuel is not new. Hell, that's why RP-1 isn't just kerosene. It needed to withstand thermal breakdown when used to cool the nozzle and other combustor parts.

Of course, the JP-7 used by the Blackbirds was pretty much non-flammable without a shot of TEB.

Only to get things started. Once the shock compression + turbine pre-heated the air the combustor had no trouble with it.

I really want Starship to happen and happen quickly - and this is really promising in terms of progress; but I think some people (on this site) are getting carried away by how quickly we're going to see the real thing. Starship / BFR is a biiiiig, complex machine, even before you start to consider it's a spaceship.

I can't speak for anyone else, but the excitement is contagious when it feels like you are watching development in real time. Hell, at one point the SpaceX Reddit had a live thread covering what was happening.

Obviously this is the prototype stage and it'll presumably reach the point where visible progress recedes to a scale of months or possibly weeks, rather than days and sometimes hours. But still, it is impressive to watch.

As an aside, when asked about whether the super heavy booster would have any kind of heat shielding, Musk replied:

Quote:

Falcon rocket booster is aluminum-lithium & carbon fiber, which have low max temperature allowables. Super Heavy booster is stainless steel. Since it only goes to around Mach 8 or 9, moreover at high altitude, it needs no heat shield, not even paint.

Only Mach 8 or 9....

It seems very odd to go with steel for the booster. They already know how to work with aluminum-lithium, and AFAIK they don't need the heat resistance of steel for the booster. So why not keep the performance since you'll be reusing the booster many times?

Did they change the cooling system again, or did I misunderstood their previous talk about using only metal and transpiration cooling?

The transpiration was only for the hottest parts. A conventional passive heatshield was to be used for the cooler locations. My understanding is there is no change. Or maybe that was just an assumption on my part. SpaceX talked a lot about the transpiration cooling but I got the impression that wasn't the entire thermal protection system.

There was also talk that seemed to indicate cooling of the outer stainless layer with circulating fluid. Possibly this in addition to the transpiration or just something they were thinking of back then. I would imagine that would also need to be vented to dump the heat though.

There is no circulation in the Starship heat shield as far as we know. In transpiration cooling the coolant gets pushed through the skin and dumped overboard. Transpiration is like sweating, circulation is like blood flow.

Right I get the differences. I am just wondering if they are using both. The tweets are not exactly super specific. Radiative cooling across 80% and active cooling on 20%. Is the vapor enough to handle all of it or do you also need to just generally cool the skin down from inside as well? Elon did say you need cryogenic liquid, the specific heat matters. Also, the cooling need is 300 degrees down into the tolerance range of the steel (around 1450 Kelvin). That still leaves an incredibly hot shell wrapped around much more delicate internal structures and fuel.

This has been tested a long time ago and the failure mode then was rapid vaporization of the test vehicle in the wind tunnel from as little as single clogged pores. Is the SpaceX design proof against that, is it susceptible to bird poop clogging? Can you rely on sweat everywhere or do you need additional cooling or a backup scheme to spread out a hot spot instead of letting it burn through?

See, I'd think the inner shell will be the structurally sound one. It's the one that's holding the cryo fuels after all. The outer shell may be thin-walled hex tiles that barely support any load one launch. The dynamic pressure from entry won't be that high in comparison to the thrust loads through the main structure.

That certainly makes sense, but I mean delicate to heat, not to load. Several minutes of 1400 K is a lot. The inner shell underneath the hexagons will not be able to radiate it away like it apparently does on the back and sides ...

I really want Starship to happen and happen quickly - and this is really promising in terms of progress; but I think some people (on this site) are getting carried away by how quickly we're going to see the real thing. Starship / BFR is a biiiiig, complex machine, even before you start to consider it's a spaceship.

I can't speak for anyone else, but the excitement is contagious when it feels like you are watching development in real time. Hell, at one point the SpaceX Reddit had a live thread covering what was happening.

Obviously this is the prototype stage and it'll presumably reach the point where visible progress recedes to a scale of months or possibly weeks, rather than days and sometimes hours. But still, it is impressive to watch.

As an aside, when asked about whether the super heavy booster would have any kind of heat shielding, Musk replied:

Quote:

Falcon rocket booster is aluminum-lithium & carbon fiber, which have low max temperature allowables. Super Heavy booster is stainless steel. Since it only goes to around Mach 8 or 9, moreover at high altitude, it needs no heat shield, not even paint.

Only Mach 8 or 9....

It seems very odd to go with steel for the booster. They already know how to work with aluminum-lithium, and AFAIK they don't need the heat resistance of steel for the booster. So why not keep the performance since you'll be reusing the booster many times?

Sending people into space is a genuinely terrible idea. In the 1960s, humanity learned that you get more information with unmanned probes that measure more accurately and function for years. Once a human is on board, the whole mission is more difficult and severely limited. The mission statement for Spacex says its ultimate goal is to allow people to live on other planets. Fair enough- but rocket engines are the least of your worries. A serious company would be working on solving the problems of how to live there not how to get there. Everything about this reeks of an attention seeking stunt.

If you can't get there then figuring out how to live there is just navel gazing. Also the cost of getting there ($/kg) is pretty damn critical. Cut the cost by 99% and a lot of things which were infeasible because very feasible. The higher the cost of transport the more expensive all your equipment is going to be.

Honestly short of academic analysis until you have some parameters on available mass to surface and the cost that will entail you can't even begin to start looking at what is the best way to use that mass.

Cut the cost enough and you can send tunneling machines, solar farms, and fleets of electrically-powered self-driving vehicles up there. If Musk was truly serious about colonizing Mars, he would devote some of his effort to these areas as well. Oh, wait. What?

BTW, Gwynne Shotwell recently jointed the board of directors of a company that makes off-road vehicles:

Coincidence?

Eh, maybe so maybe no. There's a whole lot of CEOs on boards of companies who they have no intention of forming a business relationship with. A board member gets paid a retainer plus fees and expenses for meetings, and it's one very, very easy way to rake in another $30k or so a year.

In my non-technical mind, I compare this with the approach pioneered by Burt Rutan and SpaceShipOne in the Virgin Galactic program, which used a deformable structure to massively increase drag such that the vehicle's speed bleeds away before it gets to a part of the atmosphere where re-heating becomes a concern.

You’re looking at an absolutely massive difference in energy levels. SSO/SST peaks out at around Mach 3. Super Heavy is going to re-enter somewhere around Mach 8, using the engine exhaust as a “virtual” heat shield during peak heating, as does the Falcon 9 first stage. Starship is going to re-enter at somewhere between Mach 25 and Mach 40, depending on where it’s coming from.

But I'm very interested to ask if a combination of the current SpaceX design for re-usability, coupled with maybe even disposable, deformable drag structures [think grid fins on steroids] might have been an avenue worth exploring. I make this observation in the context of Elon's statement that he needs Starship to make an instant return-to-use [i.e. allow it to cool and then just pump it full of fuel before relaunch], but that doesn't preclude disposable aerofoils.

Such drag structures add lots of mass. It you are doing horizontal landing, well then you have that mass anyway, so it only makes sense to use them that way.

Note that SSO’s design doesn’t provide a high surface area for drag, but rather makes that high drag orientation passively stable. Starship is using its legs and canards as drag flaps to maintain attitude. Shuttle and Buran used large aft planes and RCS to maintain attitude. In other words, everyone does it, but SSO did it in a way that didn’t require fly-by-wire, due to Burt Rutan’s feelings on the matter.

Starship uses a blunt body entry profile, not a lifting body it has the surface area of the propellant tanks and the payload section to provide a high surface area to mass ratio

SSO flys at something like 70deg AOA, and even though Shuttle and Shuttleski were much lower, they were still in deep stall and not behaving anything like an airfoil.

I really want Starship to happen and happen quickly - and this is really promising in terms of progress; but I think some people (on this site) are getting carried away by how quickly we're going to see the real thing. Starship / BFR is a biiiiig, complex machine, even before you start to consider it's a spaceship.

I can't speak for anyone else, but the excitement is contagious when it feels like you are watching development in real time. Hell, at one point the SpaceX Reddit had a live thread covering what was happening.

Obviously this is the prototype stage and it'll presumably reach the point where visible progress recedes to a scale of months or possibly weeks, rather than days and sometimes hours. But still, it is impressive to watch.

As an aside, when asked about whether the super heavy booster would have any kind of heat shielding, Musk replied:

Quote:

Falcon rocket booster is aluminum-lithium & carbon fiber, which have low max temperature allowables. Super Heavy booster is stainless steel. Since it only goes to around Mach 8 or 9, moreover at high altitude, it needs no heat shield, not even paint.

Only Mach 8 or 9....

It seems very odd to go with steel for the booster. They already know how to work with aluminum-lithium, and AFAIK they don't need the heat resistance of steel for the booster. So why not keep the performance since you'll be reusing the booster many times?

They do need heat resistance for the booster. Elon has said it's profile hits Mach 8. Get aluminum hot enough, and you've got to make it thicker - so you lose your strength-to-weight ratio. Also, for larger cylinders, you end up with larger wall thicknesses to prevent buckling (see SLS FSW problems). Working with steel may have just been easier than sticking with aluminum.

SpaceX had investigated carbon fiber. That's expensive, difficult to work, and also not very high temperature. Steel won the system analysis.

I really want Starship to happen and happen quickly - and this is really promising in terms of progress; but I think some people (on this site) are getting carried away by how quickly we're going to see the real thing. Starship / BFR is a biiiiig, complex machine, even before you start to consider it's a spaceship.

I can't speak for anyone else, but the excitement is contagious when it feels like you are watching development in real time. Hell, at one point the SpaceX Reddit had a live thread covering what was happening.

Obviously this is the prototype stage and it'll presumably reach the point where visible progress recedes to a scale of months or possibly weeks, rather than days and sometimes hours. But still, it is impressive to watch.

As an aside, when asked about whether the super heavy booster would have any kind of heat shielding, Musk replied:

Quote:

Falcon rocket booster is aluminum-lithium & carbon fiber, which have low max temperature allowables. Super Heavy booster is stainless steel. Since it only goes to around Mach 8 or 9, moreover at high altitude, it needs no heat shield, not even paint.

Only Mach 8 or 9....

It seems very odd to go with steel for the booster. They already know how to work with aluminum-lithium, and AFAIK they don't need the heat resistance of steel for the booster. So why not keep the performance since you'll be reusing the booster many times?

Parts of F9 need heat protection and that protection is ablative which adds cost and lengthens turnaround times. However I think the largest reason for making the booster steel is simply commonality. SpaceX has broken a lot of conventions with F9 in keeping as much common between the two stages. that improves economies of scale, gets you to market faster, and helps to build experience faster. Granted it doesn't get you bleeding edge performance but SpaceX has never been about bleeding edge performance. The metric they are most interested in is $/kg.

That certainly makes sense, but I mean delicate to heat, not to load. Several minutes of 1400 K is a lot. The inner shell underneath the hexagons will not be able to radiate it away like it apparently does on the back and sides ...

The inner walls will be at cryo temps on the inside surface so there will be quite a thermal gradient. As long as there's propellant in the tanks, the inside surface of the inside walls will never be hot. Then it's a matter of whether you can manage the thermal load on that propellant. Perhaps the engines are expecting boiling propellant instead of super-cooled on re-entry. If so, then it's just a matter of venting the gas out the top of the tank to keep the desired pressure. There's where your transpiration cooling comes from.

In my non-technical mind, I compare this with the approach pioneered by Burt Rutan and SpaceShipOne in the Virgin Galactic program, which used a deformable structure to massively increase drag such that the vehicle's speed bleeds away before it gets to a part of the atmosphere where re-heating becomes a concern.

You’re looking at an absolutely massive difference in energy levels. SSO/SST peaks out at around Mach 3. Super Heavy is going to re-enter somewhere around Mach 8, using the engine exhaust as a “virtual” heat shield during peak heating, as does the Falcon 9 first stage. Starship is going to re-enter at somewhere between Mach 25 and Mach 40, depending on where it’s coming from.

But I'm very interested to ask if a combination of the current SpaceX design for re-usability, coupled with maybe even disposable, deformable drag structures [think grid fins on steroids] might have been an avenue worth exploring. I make this observation in the context of Elon's statement that he needs Starship to make an instant return-to-use [i.e. allow it to cool and then just pump it full of fuel before relaunch], but that doesn't preclude disposable aerofoils.

Such drag structures add lots of mass. It you are doing horizontal landing, well then you have that mass anyway, so it only makes sense to use them that way.

Note that SSO’s design doesn’t provide a high surface area for drag, but rather makes that high drag orientation passively stable. Starship is using its legs and canards as drag flaps to maintain attitude. Shuttle and Buran used large aft planes and RCS to maintain attitude. In other words, everyone does it, but SSO did it in a way that didn’t require fly-by-wire, due to Burt Rutan’s feelings on the matter.

Starship uses a blunt body entry profile, not a lifting body it has the surface area of the propellant tanks and the payload section to provide a high surface area to mass ratio

SSO flys at something like 70deg AOA, and even though Shuttle and Shuttleski were much lower, they were still in deep stall and not behaving anything like an airfoil.

Wasn’t the Shuttle basically a brick during reentry?

Yes. It's best-glide ratio was something like 3/1. The simulator ran with all flaps and landing gear hanging out, plus full reverse thrust during the simulation periods.

I really want Starship to happen and happen quickly - and this is really promising in terms of progress; but I think some people (on this site) are getting carried away by how quickly we're going to see the real thing. Starship / BFR is a biiiiig, complex machine, even before you start to consider it's a spaceship.

I can't speak for anyone else, but the excitement is contagious when it feels like you are watching development in real time. Hell, at one point the SpaceX Reddit had a live thread covering what was happening.

Obviously this is the prototype stage and it'll presumably reach the point where visible progress recedes to a scale of months or possibly weeks, rather than days and sometimes hours. But still, it is impressive to watch.

As an aside, when asked about whether the super heavy booster would have any kind of heat shielding, Musk replied:

Quote:

Falcon rocket booster is aluminum-lithium & carbon fiber, which have low max temperature allowables. Super Heavy booster is stainless steel. Since it only goes to around Mach 8 or 9, moreover at high altitude, it needs no heat shield, not even paint.

Only Mach 8 or 9....

It seems very odd to go with steel for the booster. They already know how to work with aluminum-lithium, and AFAIK they don't need the heat resistance of steel for the booster. So why not keep the performance since you'll be reusing the booster many times?

I think one reason is development and constructions costs, the other is that al-li as in the F9 still means they need reentry burns to slow down, heat shields and refurbishing between flights. If going to steel makes all of this go away this will make these things much simpler, cheaper and quicker to fly, which will be important especially if they need to launch five tankers or so for each BEO mission.

I really want Starship to happen and happen quickly - and this is really promising in terms of progress; but I think some people (on this site) are getting carried away by how quickly we're going to see the real thing. Starship / BFR is a biiiiig, complex machine, even before you start to consider it's a spaceship.

I can't speak for anyone else, but the excitement is contagious when it feels like you are watching development in real time. Hell, at one point the SpaceX Reddit had a live thread covering what was happening.

Obviously this is the prototype stage and it'll presumably reach the point where visible progress recedes to a scale of months or possibly weeks, rather than days and sometimes hours. But still, it is impressive to watch.

As an aside, when asked about whether the super heavy booster would have any kind of heat shielding, Musk replied:

Quote:

Falcon rocket booster is aluminum-lithium & carbon fiber, which have low max temperature allowables. Super Heavy booster is stainless steel. Since it only goes to around Mach 8 or 9, moreover at high altitude, it needs no heat shield, not even paint.

Only Mach 8 or 9....

It seems very odd to go with steel for the booster. They already know how to work with aluminum-lithium, and AFAIK they don't need the heat resistance of steel for the booster. So why not keep the performance since you'll be reusing the booster many times?

I think one reason is development and constructions costs, the other is that al-li as in the F9 still means they need reentry burns to slow down, heat shields and refurbishing between flights. If going to steel makes all of this go away this will make these things much simpler, cheaper and quicker to fly, which will be important especially if they need to launch five tankers or so for each BEO mission.

I suspect we'll still see re-entry burns. But everything will happen at higher velocities so the gravity losses will be relatively lower.

That certainly makes sense, but I mean delicate to heat, not to load. Several minutes of 1400 K is a lot. The inner shell underneath the hexagons will not be able to radiate it away like it apparently does on the back and sides ...

The inner walls will be at cryo temps on the inside surface so there will be quite a thermal gradient. As long as there's propellant in the tanks, the inside surface of the inside walls will never be hot. Then it's a matter of whether you can manage the thermal load on that propellant. Perhaps the engines are expecting boiling propellant instead of super-cooled on re-entry. If so, then it's just a matter of venting the gas out the top of the tank to keep the desired pressure. There's where your transpiration cooling comes from.

Starship isn't all tanks and even in the tanks the residual methane and oxygen won't be much more than a wet spot. The landing propellants will be in the inner tanks not in contact with the walls.

With all the activity surrounding SS/SH and Starlink, SpaceX’s burn rate must be staggering. I hope the commercial launch, ISS resupply, Commercial Crew, and occasional USG launch profits will be enough to support both the Starlink and SS/SH side of the house...especially if there is the odd setback or two along the way.

EDIT: spelling...

7,000 employees at $200k fully loaded cost average is $1.4B/year. That's pretty hard to keep up with if you're only doing 20 something launches a year at $80-100M. Starlink really needs to pan out for them to get ahead of the run rate.

*edit*To all the downvoters, please explain in the comments which piece of information you disagree with. The fully loaded costs of engineers, scientists, and skilled trades people, the publicly published price of launches for SpaceX, or the number of launches per year.

I really want Starship to happen and happen quickly - and this is really promising in terms of progress; but I think some people (on this site) are getting carried away by how quickly we're going to see the real thing. Starship / BFR is a biiiiig, complex machine, even before you start to consider it's a spaceship.

I can't speak for anyone else, but the excitement is contagious when it feels like you are watching development in real time. Hell, at one point the SpaceX Reddit had a live thread covering what was happening.

Obviously this is the prototype stage and it'll presumably reach the point where visible progress recedes to a scale of months or possibly weeks, rather than days and sometimes hours. But still, it is impressive to watch.

As an aside, when asked about whether the super heavy booster would have any kind of heat shielding, Musk replied:

Quote:

Falcon rocket booster is aluminum-lithium & carbon fiber, which have low max temperature allowables. Super Heavy booster is stainless steel. Since it only goes to around Mach 8 or 9, moreover at high altitude, it needs no heat shield, not even paint.

Only Mach 8 or 9....

It seems very odd to go with steel for the booster. They already know how to work with aluminum-lithium, and AFAIK they don't need the heat resistance of steel for the booster. So why not keep the performance since you'll be reusing the booster many times?

I think one reason is development and constructions costs, the other is that al-li as in the F9 still means they need reentry burns to slow down, heat shields and refurbishing between flights. If going to steel makes all of this go away this will make these things much simpler, cheaper and quicker to fly, which will be important especially if they need to launch five tankers or so for each BEO mission.

I suspect we'll still see re-entry burns. But everything will happen at higher velocities so the gravity losses will be relatively lower.

Musk has stated the booster won't need a reentry burn. It's early days though, so who knows.

I really want Starship to happen and happen quickly - and this is really promising in terms of progress; but I think some people (on this site) are getting carried away by how quickly we're going to see the real thing. Starship / BFR is a biiiiig, complex machine, even before you start to consider it's a spaceship.

I can't speak for anyone else, but the excitement is contagious when it feels like you are watching development in real time. Hell, at one point the SpaceX Reddit had a live thread covering what was happening.

Obviously this is the prototype stage and it'll presumably reach the point where visible progress recedes to a scale of months or possibly weeks, rather than days and sometimes hours. But still, it is impressive to watch.

As an aside, when asked about whether the super heavy booster would have any kind of heat shielding, Musk replied:

Quote:

Falcon rocket booster is aluminum-lithium & carbon fiber, which have low max temperature allowables. Super Heavy booster is stainless steel. Since it only goes to around Mach 8 or 9, moreover at high altitude, it needs no heat shield, not even paint.

Only Mach 8 or 9....

It seems very odd to go with steel for the booster. They already know how to work with aluminum-lithium, and AFAIK they don't need the heat resistance of steel for the booster. So why not keep the performance since you'll be reusing the booster many times?

The Falcon 9 first stage needs to do a reentry burn to survive its slower reentry and despite this it still has special features on its ass to reduce wear and tear.

An all stainless steel SH can get away with shorter or maybe even no reentry burn and still have no need for maintenance. At worse stainless steel allows fast cheap turnaround, at best it actually outperforms an aluminum based architecture. Either way commonality with SS in manufacturing is an important economic consideration.